File sensor does not show up in entities

hello,

i just created a file sensor

- platform: file
  file_path: /config/tmp/reset-lg-devmode-timer_result.txt
  name: lgdevresult
  value_template: "{{ value_json.result }}"

but it won’t show up in entities.
and when I try to read the state like this

{{ states('sensor.lgdevresult') }}

it returns unknown.
So I doubt this one works.

What should I do to make this file sensor work?

If the value json does not resolve, the sensor will not exist.
Did you check logs?

I actually needed to restart HA core fully, not only “quick reload”